Systems and methods for repairing soft tissues using nanofiber material

ABSTRACT

An anchoring system is a combination of a nanofiber scaffold material and an arthroscopically deployable suture anchor. The anchor is deployed into a bone tunnel using common techniques. The nanofiber material extends out of the proximal end of the implant, once deployed. The implant also includes pre-loaded sutures or has the ability to accept and lock sutures to the implant. For an implant pre-loaded with suture, the implant is placed into the bone, the material is deployed above the anchor onto the surface of the bone, suture is passed through the soft tissue, and knots are tied to secure the tissue against the bone, sandwiching the material between the bone and tissue, to provide a pathway for cells from the bone marrow to the soft tissue-bone interface, promote the healing response, provide a biomimetic structure that cells readily adhere to, and create a larger healing footprint.

This application claims the benefit under 35 U.S.C. 119(e) of the filingdate of Provisional U.S. Application Ser. No. 61/713,230, entitledSystems and Methods for Repairing Soft Tissues Using Nanofiber Material,filed on Oct. 12, 2012, which application is herein expresslyincorporated by reference, in its entirety.

BACKGROUND OF THE INVENTION

Rotator cuff repair is the most common surgical repair performed in theshoulder, with more than 270,000 repairs performed annually in theUnited States, as of 2006, with that number expected to increaseannually with concurrent increase in the aging population. Advances inrotator cuff repair technique have focused principally on transitionfrom open repair, to mini-open repair, and more recently to fullyarthroscopic repair. Moreover, advances have been made in suturepatterns or arthroscopic repairs to better recreate the naturalfootprint insertion of the rotator cuff to improve time-zero mechanicalproperties, and in hopes of improving the healing rates.

In spite of improvements in surgical technique, healing rates asevidenced by postoperative ultrasound or MRI have varied widely, rangingfrom 91% healing rates in small tears to healing rates of only 10% inthe largest tears. It is believed that healing rates are low due to theinadequate re-creation of the natural anatomic bone-tendon interface.

Various techniques have been employed to improve interface healing,including mesenchymal stem cells, xenograft, allograft, and acellularnanofiber scaffolds. Advances in nanofiber technology may hold promisein improving the bone-tissue interface healing of many soft tissueinjuries, and have several advantages over other proposed methods.Issues of procurement, scalability, ease of use, and integration withcurrently performed surgical repair methods favor the nanofiberscaffolds.

Usage of acellular augmentation devices have been evaluated in animalmodels, demonstrating safety to the animal and effectiveness inimproving the soft tissue healing. Yokoya et al. (“Tendon-Bone InsertionRepair and Regeneration Using Polyglycolic Acid Sheet in the RabbitRotator Cuff Injury Model”, American Journal of Sports Medicine, Vol.36, no. 7, pp 1298-1309, 2008) used a polyglycolic acid (PGA) sheet toaugment rotator cuff repairs of infraspinatus tendons in Japanese whiterabbits, showing histological improvement in fibrocartilage layering anda slight improvement in tensile strength when compared to controltendons. Funakoshi et al. (“Rotator Cuff Regeneration Using ChitinFabric as an Acellular Matrix”, Journal of Shoulder and Elbow Surgery,Vol. 15, No. 1, pp. 112-118, 2006) demonstrated increased fibroblastpresence and collagen formation when synthetic extracellular matrix wassurgically applied to rotator cuff tears in Japanese white rabbits.MacGillivray et al. (“Biomechanical Evaluation of a Rotator Cuff DefectModel Augmented with a Bioresorbable Scaffold in Goats”, Journal ofShoulder and Elbow Surgery, Vol. 15, No. 5, pp. 639-644, 2006) usedpolylactic acid patches in goats, showing safety to the animal butminimal difference between the treated and control groups. A similarexperiment using a woven poly-L-lactide device was performed by Derwinet al. (“Rotator Cuff Repair Augmentation in a Canine Model with Use ofa Woven Poly-L-Lactide Device”, Journal of Bone and Joint Surgery A,Vol. 91, No. 5, pp. 1159-1171, 2009) in a dog model. A portion of eachinfraspinatus tendon was removed from the rotator cuff and then repairedin both shoulders. In one shoulder, a woven poly-L-lactide device wasplaced over the repair. In the other shoulder, the repair was leftunaugmented. The augmented rotator cuff repair resulted in fewer tendonretractions, greater strength, and increased stiffness when compared tothe contralateral untreated rotator cuff repairs.

In an attempt to improve the healing of the tissue-bone interface,acellular nanofiber scaffolds have been studied. Nanofiber scaffolds aretypically made from materials with well-known biologic properties. Forexample, poly-lactide-co-glycolide (PLGA) is a material commonly used inabsorbable sutures and medical devices. PLGA can be fashioned viaelectrospinning into nanofiber sheets, which in turn can be interposedbetween a torn tendon and the underlying bone attachment site duringsurgical tissue repair. Additionally, other polymers that arenon-absorbable have been used as nanofiber scaffolds as well. When usedin this manner it should be noted that the nanofiber is not acting as astructural graft under tension. The interposed fibers are used only as ascaffold to support ingrowth of host cells.

Moffat et al (“Novel Nanofiber-Based Scaffold for Rotator Cuff Repairand Augmentation”, Tissue Eng Part A, Vol. 14, pp. 1-12, 2008) used anin vivo model to study the potential for an aligned nanofiber sheet topromote fibroblast formation and improved mechanical properties. Theyfound that “mechanical properties of the aligned nanofiber scaffoldswere significantly higher than those of the unaligned, and although thescaffolds degraded in vitro, physiologically relevant mechanicalproperties were maintained. These observations demonstrate the potentialof the PLGA nanofiber-based scaffold system for functional rotator cuffrepair. Moreover, nanofiber organization has a profound effect oncellular response and matrix properties, and it is a critical parameterfor scaffold design.” Some controversy exists over the best nanofiberarchitecture: monophasic, biphasic, or even triphasic.

Implantation of sheets of material as studied by Moffat, Derwin,MacGillivray, Funakoshi, and others requires an open surgical procedure.The current standard-of-care for rotator cuff repair is an arthroscopicprocedure, growing from less than ten percent of all rotator cuffrepairs in 1996 to almost sixty percent of all rotator cuff repairs in2006. The trend has continued in the past 6 years, with currentestimates suggesting that greater than 85% of rotator cuff repairs areperformed arthroscopically. Further improvements to the procedure thatare potentially offered by devices and/or materials as described byMoffat must be compatible with arthroscopic implantation methods inorder to be widely accepted.

Rotator cuff repair surgery has evolved from predominately beingperformed with an open procedure to an arthroscopic procedure during thepast 15 years. The current state-of-the art arthroscopic proceduregenerally utilizes one of the following approaches:

a) as shown in FIG. 1, a single row of suture anchors 1 lying underneaththe rotator cuff tendon 2 with sutures passed up through the tendon andsecurely tied to anchor the tendon to the bone 3;

b) as shown in FIG. 2, a double row of suture anchors 1 lying underneaththe rotator cuff tendon 2 with sutures passed up through the tendon andsecurely tied to anchor the tendon to the bone;

c) as shown in FIG. 3, a single row of suture anchors 1 lying underneaththe rotator cuff tendon 2 with sutures passed up through the tendon,securely tied, with suture from knots extending laterally over thetendon and secured to the bone 3 with a knotless suture anchor 4 that isoutside the margin of the tendon.

There are no prospective, randomized published studies that show adifference in outcome between the three procedure groups listed aboveand depicted in FIGS. 1-3, and in spite of improvements in surgicaltechnique, failure rates (defined as the tendon not healing to the bone)as evidenced by postoperative ultrasound or MRI have varied widely,range from 9% in small tears, to 90% in the largest tears. It isbelieved that failure to heal is due to the inadequate re-creation ofthe natural anatomic bone-tendon interface.

Various techniques have been employed to improve interface healing,including mesenchymal stem cells, xenografts, allografts, and acellularnanofiber scaffolds. Advances in nanofiber technology may hold promisein improving the bone-tissue interface healing of many soft tissueinjuries, and have several advantages over other proposed methods.Issues of procurement, scalability, ease of use, and integration withcurrently performed surgical repair methods favor the nanofiberscaffolds.

A product that combines the current arthroscopically-placed sutureanchor implants with a nanofiber scaffold, as disclosed and describedherein, will allow the surgeon to repair the rotator cuff using currentarthroscopic methods.

SUMMARY OF THE INVENTION

As noted above, this invention is a combination of a nanofiber scaffoldmaterial and an arthroscopically deployable suture anchor and isintended to improve soft tissue-to-bone repair. The suture anchor isdeployed into a bone tunnel using common arthroscopic surgicaltechniques. The nanofiber material extends from a location within thebone tunnel, out of the proximal end of the implant, to a portion of thematerial external to the bone surface, once deployed. The implant alsoincludes pre-loaded sutures or has the ability to accept and locksutures to the implant. For an implant pre-loaded with suture, theimplant is placed into the bone, the material is deployed above theanchor onto the surface of the bone, suture is passed through the softtissue, and knots are tied to secure the tissue against the bone,sandwiching the material between the bone and tissue. The suture anchorwith nanofiber material improves the current repair in at least thefollowing ways:

a) the material in the inventive system provides a pathway for cellsfrom the bone marrow to the soft tissue-bone interface, accelerating andpromoting the healing response;

b) the inventive system provides a biomimetic structure that cellsreadily adhere to; and

c) the inventive system creates a larger healing footprint than with asuture anchor alone.

More particularly, there is disclosed an anchoring system for securingsoft tissue to bone, which comprises an implant having a body forsecurement to bone and an insert comprising a nanofiber materialattached to the implant body and having an extended surface forcontacting the soft tissue. The implant further comprises externalsurface features, threads in the illustrated embodiments, for securingthe implant within surrounding bone. The extended surface of the insertcomprises a head formed of the nanofiber material, the nanofibermaterial being flexible so that the head is extendable from anundeployed retracted position to a deployed extended position.

The insert further comprises a portion extending distally from the headfor securement to the anchor body. The insert distal portion comprises atube of material and the head comprises a plurality of strips extendingfrom a proximal end of the tube. The insert distal portion comprises thenanofiber material, which is mono-phasic in one embodiment.

In another aspect of the invention, there is disclosed an insert for usein a soft tissue anchoring system. The insert comprises an extendedportion having an extended surface for engaging the soft tissue to beanchored, and a second portion for securing the extended portion to abone anchor. The extended portion of the insert comprises a nanofibermaterial. The extended surface of the insert comprises a head formed ofthe nanofiber material, the nanofiber material being flexible so thatthe head is extendable from an undeployed retracted position to adeployed extended position for insertion into a procedural site. Thesecond portion extends distally from the head for securement to a bodyof the bone anchor. The insert distal portion comprises a tube ofmaterial and the head comprises a plurality of strips extending from aproximal end of the tube. The insert second portion comprises thenanofiber material, wherein in one embodiment, the nanofiber material ismono-phasic.

In still another aspect of the invention, there is disclosed a methodfor securing soft tissue to bone, which comprises a step of inserting animplantable anchor having a body into a desired bone site, deploying aportion of a nanofiber insert secured to the anchor to an extendedconfiguration, and approximating the soft tissue to the bone so that thesoft tissue engages the extended portion of the nanofiber insert.

The inserting step comprises placing the body of the implantable anchorinto a bone tunnel and securing the body in place by engaging externalfeatures on the anchor body with adjacent bone. The approximating stepcomprises tensioning suture extending from the anchor body through thesoft tissue to draw the soft tissue into close proximity with the bone,and then knotting free ends of the suture. The deploying step comprisesremoving a sheath constraining the nanofiber insert portion so that itexpands to its extended configuration.

The invention, together with additional features and advantages thereof,may best be understood by reference to the following description takenin conjunction with the accompanying illustrative drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a first prior art approach forrepairing a rotator cuff;

FIG. 2 is a schematic drawing of a second prior art approach forrepairing a rotator cuff;

FIG. 3 is a schematic drawing of a third prior art approach forrepairing a rotator cuff;

FIG. 4 is a schematic plan view of a system and method for repairingsoft tissues in accordance with the principles of the present invention;

FIG. 5 is an isometric view of the system shown in FIG. 4;

FIG. 6A is an isometric view of one embodiment of a nanofiber deviceaccording to the present invention;

FIG. 6B is a plan view of the device of FIG. 6A;

FIG. 6C is a top view of the device of FIGS. 6A and 6B;

FIG. 7A is an isometric view of another embodiment of a nanofiber deviceaccording to the present invention;

FIG. 7B is a plan view of the device of FIG. 7A; and

FIG. 7C is a top view of the device of FIGS. 7A and 7B.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to FIGS. 4-7B, the inventive system andmethods utilize nanofiber material which is incorporated into the sutureanchor and deployed into the bone using standard arthroscopic surgicaltechniques. Once deployed, the material is located between the softtissue and bone.

FIGS. 4 and 5 illustrate the implementation of a soft tissue anchoringsystem 10 in accordance with the present invention. What is illustratedis a portion of soft tissue 12 which is to be attached to a portion ofbone 14 using the anchoring system 10. The soft tissue 12 may comprise arotator cuff tendon, to be secured to the humerus, as discussed above inconjunction with FIGS. 1-3, or the invention is equally applicable toany other site wherein attachment of soft tissue to bone is desired. Abone tunnel 16 is created in the bone 14 and a suture anchor 18 isplaced within the bone tunnel 16, as shown, using common surgicaltechniques, which may or may not be arthroscopic. The illustrated sutureanchor 18 comprises a hollow anchor body, having threads 20 or othersuitable structure for engaging adjacent bone forming walls of thetunnel 16 to fix the anchor 18 in place within the tunnel. This type ofcorkscrew suture anchor is well known in the art. Other suitable typesof suture anchors may also be employed. The suture anchor also has aneyelet 22 or other suitable structure for securing suture 24 to theanchor, which suture extends through the soft tissue 12 and securedthereto by means of a knot 26 or other suitable means. Thus, the softtissue 12 is secured to the adjacent bone 14 by extending the free endsof the suture 24 through the soft tissue 12, securing the anchor 18within the bone tunnel 16, tensioning the suture 24 until the softtissue 12 is approximated to the adjacent bone 14, then creating thesuture knot 26 to secure the soft tissue in place. This basic techniqueis well known in the art.

The present inventive system comprises a member or insert 28 which iscomprised of a nanofiber material. More particularly, the nanofibermaterial is, in one embodiment, a monophasic nanofiber scaffold, whichare known in the art, as described in the prior art references discussedin the Background portion of this application. Alternatively, amulti-phasic nanofiber scaffold, such as disclosed and described in U.S.Published Patent Application No. 2010/0292791 to Lu et al., hereinexpressly incorporated by reference in its entirety, may be used. Thenanofiber scaffold member 28 extends into the bone tunnel 16 through thehollow center of the anchor 18, and expands outwardly at the bonesurface to maximize surface area contact between the tissue and bone.

Material Configuration and Deployment

There are many configurations which the inventive nanofiber member 28may assume. Two such alternative examples are illustrated in FIGS. 6A-6Cand FIGS. 7A-7C, respectively. Each configuration shows the material inthe deployed state. Prior to deployment of the anchor into the bone, thematerial is rolled in a cylindrical fashion around the implant insertershaft and held in place (and protected) by a tubular sheath. This allowsthe use of traditional arthroscopic surgical techniques to place theimplant into the bone. Once the implant is placed into the bone, thesheath is retracted and the nanofiber material is spread out to maximizethe surface area contact between the tissue and bone.

Material Orientation

The nanofiber material can be manufactured with the fibers organized ina random orientation (unaligned) or aligned in one direction (aligned).There are three primary reasons why fiber alignment is important whencoupled with the suture anchor:

a) As shown by Moffat, aligned fibers provide a pathway for faster cellgrowth and travel. One presently preferred configuration has a scaffoldwith fibers aligned axially within the anchor in the direction of celltravel from the bone marrow to the bone surface.

b) Fiber orientation can be controlled to mimic the tissue beingrepaired. For example, the rotator cuff (supraspinatus) has linearlyoriented fibers. The scaffold material exposed to the supraspinatus mayhave aligned fibers in the same direction as the tissue, thus promotingfaster and more complete tissue ingrowth. Markings on the inserter oranchor may facilitate proper alignment of the material to the tissue.

c) Fiber orientation determines the mechanical strength of the scaffoldmaterial. Aligned material has high tensile strength in the direction ofthe fibers and weak tensile strength in the direction perpendicular tothe fibers. Unaligned material exhibits tensile strength in between thatof aligned material pulled in two perpendicular directions. The materialcan be constructed and oriented in the anchor in such a way to increasethe strength where necessary.

Material Attachment

There are several ways the material may be attached to an implant. Forimplants pre-loaded with suture, the material may be looped around thesame eyelet as the suture or passed around a secondary eyelet. Anothermethod for attachment is mechanically fastening the material to theanchor using a cleat, screw or post. The material may also be pinchedbetween two halves of an implant. The material may be attached to aportion of an implant using a knot or adhesive. The material may also bebonded to the implant with the use of solvent.

As noted above, two exemplary embodiments of the present inventivesystem are illustrated in FIGS. 6A-6C and 7A-7C, respectively. In eachembodiment, the nanofiber insert 28 comprises a distal portion or shaft30 for attaching the insert 28 to the anchor 18, and a proximal head 32.As shown in FIGS. 4 and 5, the insert 28, when the suture anchor isdeployed, is disposed so that the distal portion 30 extends through thesuture anchor 18, as shown. A proximal end of the distal portion 30extends proximally of the proximal end of the anchor body, and the head32 is disposed at a proximal end of the insert distal portion, as shown.

FIGS. 6A-6C illustrates an embodiment wherein the insert distal portion30 comprises a tube of material with strips 34 cut in the proximal endto allow the material to be deployed and spread out radially, as shown,to form the proximal head 32 and increase the surface contact betweenthe tissue and bone. The tube comprises the distal portion 30 which issecured to the implant. FIGS. 7A-7C illustrates an alternativeembodiment, wherein the insert 28 comprises a die-cut sheet material inthe deployed condition. The long portions form the distal portion 30which is disposed within the implant that is deployed into bone.

Additional Embodiments and Applications

An additional embodiment of the invention is an implant as previouslydescribed, with nanofiber material fixed solely to the proximal end(proximal defined as the end of the implant that is adjacent to the softtissue, and distal defined as the end of the implant farthest in thebone). The nanofiber material covers just the surface area of theproximal end of the implant or possibly extends further proximallyand/or radially away from the central axis of the implant.

Another additional embodiment of the invention is an implant aspreviously described, wherein the nanofiber material is fixedmechanically, with an adhesive, or by solvent bonding.

Yet another additional embodiment of the invention is an implant aspreviously described wherein the method of attachment of the material tothe implant is via the use of a suture tether that is attached to theimplant and the material. The material may be either fixed or movable.To enable the material to be moved into position, the suture isconfigured such that the surgeon pulls on the free end of the suturewhich moves the material closer to the implant, allowing the surgeon toposition the material into a desired location. The position of thematerial relative to the implant is set prior to insertion of theimplant into the bone or after the implant is deployed into the bone.Once the material is in position it is locked in place or reversiblymovable. This may also be incorporated into two or more implants toallow the material to be placed in an adjustable location determined bythe surgeon on the bone in between two or more implants.

Still another additional embodiment of the invention is an implant aspreviously described, wherein the nanofiber material is containedinternal to the implant, along its central axis. The material extends ator near the distal tip and at, near or beyond the proximal end of theimplant.

Another additional embodiment of the invention is an implant aspreviously described wherein the material may also be containedexternally to the implant or within external channels.

Yet another additional embodiment of the invention is two or moreimplants as previously described with a bridge of nanofiber materialstrung between each implant. This configuration might best be describedas a blanket of nanofiber material anchored at each implant, with thenanofiber material incorporated within or along the exterior of theimplants.

Other applications of the invention include, but are not limited to,applications where soft tissue is re-attached surgically orarthroscopically to bone in locations such as knee, shoulder, foot,ankle, elbow, wrist, hand, spine, and hip. Surgical specialties thatcould utilize the invention include sports medicine, trauma, spine, footand ankle, hand, hip, and extremities.

Moffat and others have shown that the use of nanofiber scaffolds promotecell attachment and growth in both aligned and unaligned orientations.The present invention improves the ease of use of nanofiber scaffoldsfor surgeons by pre-attaching the scaffold to a current,state-of-the-art suture anchor that can be implanted using standardarthroscopic procedures.

Arthroscopic surgeons do not want to complicate their surgicalprocedures. The value of nanofiber scaffolds in sheet form as proposedby Moffat will be substantially diminished due to the fact that surgeonswill be reluctant to use a product that requires an open surgicalprocedure versus an arthroscopic procedure. The present inventionfacilitates arthroscopic use of nanofiber scaffolds, potentiallyincreasing their value by several fold.

Accordingly, although an exemplary embodiment of the invention has beenshown and described, it is to be understood that all the terms usedherein are descriptive rather than limiting, and that many changes,modifications, and substitutions may be made by one having ordinaryskill in the art without departing from the spirit and scope of theinvention, which is to be limited only in accordance with the followingclaims.

What is claimed is:
 1. An anchoring system for securing soft tissue tobone, comprising an implant having a body for securement to bone and aninsert comprising a nanofiber material attached to the implant body andhaving an extended surface for contacting the soft tissue.
 2. Theanchoring system as recited in claim 1 wherein the implant furthercomprises external surface features for securing the implant withinsurrounding bone.
 3. The anchoring system as recited in claim 2, whereinthe external surface features comprise threads.
 4. The anchoring systemas recited in claim 1, wherein the extended surface of the insertcomprises a head formed of said nanofiber material, the nanofibermaterial being flexible so that the head is extendable from anundeployed retracted position to a deployed extended position.
 5. Theanchoring system as recited in claim 4, wherein the insert furthercomprises a portion extending distally from said head for securement tothe anchor body.
 6. The anchoring system as recited in claim 5, whereinsaid insert distal portion comprises a tube of material and said headcomprises a plurality of strips extending from a proximal end of thetube.
 7. The anchoring system as recited in claim 5, wherein the insertdistal portion comprises said nanofiber material.
 8. The anchoringsystem as recited in claim 1, wherein said nanofiber material ismono-phasic.
 9. An insert for use in a soft tissue anchoring system,comprising: an extended portion having an extended surface for engagingthe soft tissue to be anchored; and a second portion for securing theextended portion to a bone anchor; wherein the extended portion of theinsert comprises a nanofiber material.
 10. The insert as recited inclaim 9, wherein the extended surface of the insert comprises a headformed of said nanofiber material, the nanofiber material being flexibleso that the head is extendable from an undeployed retracted position toa deployed extended position for insertion into a procedural site. 11.The insert as recited in claim 10, wherein the second portion extendsdistally from said head for securement to a body of the bone anchor. 12.The insert as recited in claim 11, wherein said insert distal portioncomprises a tube of material and said head comprises a plurality ofstrips extending from a proximal end of the tube.
 13. The insert asrecited in claim 11, wherein the insert second portion comprises saidnanofiber material.
 14. The insert as recited in claim 1, wherein saidnanofiber material is mono-phasic.
 15. A method for securing soft tissueto bone, comprising: inserting an implantable anchor having a body intoa desired bone site; deploying a portion of a nanofiber insert securedto the anchor to an extended configuration; and approximating the softtissue to the bone so that the soft tissue engages the extended portionof the nanofiber insert.
 16. The method as recited in claim 15, whereinthe inserting step comprises placing the body of the implantable anchorinto a bone tunnel and securing the body in place by engaging externalfeatures on the anchor body with adjacent bone.
 17. The method asrecited in claim 15, wherein the approximating step comprises tensioningsuture extending from the anchor body through the soft tissue to drawthe soft tissue into close proximity with the bone, and then knottingfree ends of the suture.
 18. The method as recited in claim 15, whereinthe deploying step comprises removing a sheath constraining thenanofiber insert portion so that it expands to its extendedconfiguration.